To add new gems (external tools/libraries written in Ruby) you can edit the Gemfile_custom file. For example, to add the rails-footnotes gem you would add:
gem "rails-footnotes","~> 4.0"
And then run bundle install and follow any gem specific installation steps from its documentation.
Note: it's possible to stumble into conflicts when updating to a new Consul version. In repositories where you haven't added many custom gems, first accept the Gemfile.lock from the new version of Consul and then run bundle install. In general, it's recommended to be specific with the versions when defining gems in Gemfile_custom. That way, you won't upgrade these gems when running bundle install.
